efl_ui_widget: ensure that tree_unfocusable is binary number in its getter

since 2dd596084b, tree_unfocusable is changed from
Eina_Bool to int.
Double negation ensure binary return value of `elm_widget_tree_unfocusable_get`

Reviewed-by: Marcel Hollerbach <mail@marcel-hollerbach.de>
Differential Revision: https://phab.enlightenment.org/D9673

src/lib/elementary/efl_ui_widget.c

@@ -1776,7 +1776,7 @@ elm_widget_tree_unfocusable_get(const Eo *obj)
    Elm_Widget_Smart_Data *sd = efl_data_scope_safe_get(obj, MY_CLASS);
    if (!sd) return EINA_FALSE;
 
-   return sd->tree_unfocusable;
+   return !!sd->tree_unfocusable;
 }
 
 /**